What happens during burning?

Burning is a very fast chemical reaction in which a fuel combines with oxygen, releasing heat and light. Each substance has its own ignition temperature. Thus, some substances which have a low ignition temperature catch fire easily, while others with a high ignition temperature catch fire with difficulty. The size of the surface is also important, which reacts with the oxygen in air. A big log of wood cannot be ignited with a single matchstick, but fine wood shavings can be ignited very easily. A flame arises only when a substance burns in the gaseous state. In case of wood, the oil vapours in the wood burn, which give the typical smell of the wood?